A conventional electronic tuner is described hereinafter with reference to FIG. 4, as an example of a conventional high-frequency signal transmission apparatus.
FIG. 4 shows a conventional electronic tuner. In the drawing, high-frequency (HF) signals that have been modulated by television signals are fed into low-noise HF amplifier 102, via input terminal 101. Fed into mixer 105 are the output of HF amplifier 102 and the output of local oscillator 104. The output of this mixer 105 is fed into band-pass filter 106. In turn, the output of band-pass filter 106 is fed into intermediate-frequency (IF) amplifier 107. The output of this IF amplifier 107 and the output of local oscillator 108 are fed into mixer 109. In turn, the output of this mixer 109 is fed into band-pass filter 110. IF amplifier 111 amplifies the output of band-pass filter 110. The output signals from IF amplifier 111 are supplied via output terminal 112. The conventional electronic tuner is structured as above.
All these components are connected to provide a low impedance of approx. 50 Ω and made of unbalanced circuits. However, there is a problem. Because the HF signal transmission apparatus for use in such a conventional electronic tuner is made of components having a low impedance of 50 Ω, a large current flowing therethrough causes large power consumption. Further, because all the components are made of unbalanced circuits, an amplitude that a single active element can handle is small. Therefore, a plurality of amplifiers are required to amplify the signals to a large degree. This results in a problem of large power consumption.